Changes in beta-2 adrenergic receptor and AMP-activated protein kinase alpha-2 subunit in the rat vestibular nerve after labyrinthectomy

In the present study, to elucidate the role of vestibular ganglion (VG) after the unilateral labyrinthine damage, we examined quantitative changes in mRNA expression of beta-adrenergic receptors (bARs) and AMP-activated protein kinase alpha catalytic subunits (aAMPKs) in VG after unilateral labyrinthectomy (UL) in rats. Using the real-time PCR method, beta2 AR mRNA expression in bilateral VG and AMPK alpha2 mRNA expression in the ipsilateral VG were significantly up-regulated with the maximum increase at the postoperative 7 day and 1 day, respectively. The up-regulation of beta2 AR in bilateral VG was long-lasting until 28 days after UL and that of AMPK alpha2 in the ipsilateral VG was just transient within 7 days after UL. These mRNA changes were supported by immunohistochemical data. According to previous reports, both of bARs and aAMPKs could regulate mitochondrial uncoupling protein (UCP) mRNA expression in several kinds of tissues and therefore might have thermogenic neurotransmission and antioxidant neuroprotective roles in neuronal tissues. UL requires not only long-lasting response of VG for central vestibular neuro-plasticity around 2–4 weeks but rapid response of VG against apoptosis of peripheral vestibular epithelia-neuronal synapses. The present findings suggest that beta2 AR in bilateral VG and AMPK alpha2 in the ipsilateral VG might play important signaling roles after the unilateral labyrinthine damage.

► Delayed up-regulation and long-lasting increase of beta2 adrenergic receptor in bilateral vestibular ganglion (VG) cells could play an important signaling role in bilateral sides after unilateral labyrinthectomy (UL).
► Rapid and transient increase of AMP-activated protein kinase alpha2 in the ipsi-lateral VG cells could play an important signaling role in the lesioned side after UL.
► Especially, the present result that UL induced long-lasting molecular responses in the contra-lateral VG cells, is very unique and never seen before in this research field.